ASN Report 2020

risks and can lead to dissemination of radioactive material, a potential source of internal and external contamination for the operators who work at close range and must be protected. This work can moreover be carried out near radiation sources, which increases the risk of external exposure for the workers. 2.2.2 Research reactors Nine experimental reactors are in final shutdown status at the end of 2020: Rapsodie (sodium-cooled fast neutron reactor), Masurca (critical mock-up), Phébus (experimental reactor), Osiris, Orphée (“pool” type reactors), Éole and Minerve (critical mock-ups), Ulysse and Isis (training reactors). They are all in the decommissioning preparation phase, except for Ulysse, whose decommissioning was completed in August 2019. These reactors are characterised by a lower power output – from 100 Watts thermal (Wth) to 70 MWth – than the nuclear power reactors. When they were designed back in the 1960s to 1980s, the question of their decommissioning was not considered. One of the major decommissioning problems is the loss of memory of the design and operation of the installation. Therefore maintaining skills and the installation characterisation phase to determine its initial state (state of the installation at the start of decommissioning) are of vital importance. At the time of decommissioning, these installations usually present a low radiological source term, as one of the first operations consists in removing the spent fuel during the decommissioning preparation operations. The risks involved in research reactor decommissioning operations evolve rapidly due to the numerous changes in the installation. The nuclear risks gradually give way to conventional industrial risks, such as the risk associated with the simultaneous management of several worksites, or the chemical risks during the clean-out- phase. One of the main challenges comes from the production and management of large volumes of VLL waste, which must be stored then disposed of via an appropriate route. There is a considerable amount of decommissioning experience feedback for the research reactors, given the decommissioning of numerous similar installations in France (Siloé, Siloette, Mélusine, Harmonie, Triton (4) , the Strasbourg University Reactor – RUS) and abroad. Their dismantling time-frames usually span about ten years. Most of these reactors were demolished with conventional disposal following clean-out. 2.3  The front-end “nuclear fuel cycle” facilities Two front-end “nuclear fuel cycle” facilities are undergoing decommissioning. They are situated on the Tricastin site, one specialising in uranium enrichment by gaseous diffusion (BNI 93), the other in uranium conversion (BNI 105). The only radioactive materials used in these plants were uranium- bearing substances. One of the particularities of these facilities lies in the presence of radioactive contamination associated with the presence of “alpha” particle-emitting uranium isotopes. The radiation exposure risks are therefore largely linked to the risk of internal exposure. Furthermore, these are older facilities whose operating history is poorly known. Determining the initial state, particularly the pollution present in the soils beneath the structures, therefore remains an important issue. Furthermore, the industrial processes used at the time involved large quantities of toxic chemical substances (uranium, chlorine trifluoride and hydrogen fluoride, for example): the containment of these chemical substances is thus also an issue in these facilities. 4. Triton was one of the first very compact and very flexible pool type research reactors called Material Test Reactor (MTR). Triton (6.5 MWth) was installed in Fontenay‑aux‑Roses in 1959. 2.4  The back-end “nuclear fuel cycle” facilities The back-end facilities of the “nuclear fuel cycle” are the spent fuel storage pools, the spent fuel reprocessing plants and the facilities for storing waste from the treatment process. These facilities are operated by Orano and situated on the La Hague site. The first processing facility at La Hague was commissioned in 1966, initially for reprocessing the fuel from the first-generation GCRs. This facility, BNI 33, called UP2-400 standing for “Production Unit No. 2-400 tonne” (the first reprocessing plant was UP1 situated in the DBNI of Marcoule and is currently being decommissioned), was definitively shut down on 12 January 2004 along with its support facilities, namely the effluent treatment station STE2 and the spent fuel reprocessing facility AT1 (BNI 38), the radioactive source fabrication facility ELAN IIB (BNI 47) and the “High Activity Oxide” facility (HAO), built for reprocessing the fuels from the “light water” reactors (BNI 80). Unlike the direct on-line packaging of the waste generated by the UP2-800 and UP3-A plants in operation, most of the waste generated by the first reprocessing plant was stored without treatment or packaging. Decommissioning is therefore carried out concomitantly with the legacy Waste Retrieval and Packaging (WRP) operations. This waste is highly irradiating and comprises structural elements from fuel reprocessing, technological waste, rubble, soils and sludge. Some of the waste has been stored in bulk with no prior sorting. The retrieval operations therefore require remotely operated pick-up means, conveyor systems, sorting systems, sludge pumping and waste packaging systems. The development of these means and carrying out the operations under conditions ensuring a satisfactory level of safety and radiation protection represent a major challenge for the licensee. Given that these operations can last several decades, the management of ageing is also a challenge. Taking into account the quantities, the physical and chemical forms and the radiotoxicity of the waste contained in these facilities, the licensee must develop means and skills that involve complex engineering techniques (radiation protection, chemistry, mechanics, electrochemistry, robotics, artificial intelligence, etc.). At present about ten projects of this type are underway in the former facilities. They will span several decades and are a prerequisite to the complete decommissioning of these facilities, whereas the decommissioning of the process parts of the plant is continuing with more conventional techniques. 2.5  The support facilities (storage and processing of radioactive effluent and waste) Many of these facilities, most of which were commissioned in the 1960’s and whose level of safety does not comply with current best practices, have been shut down. Old storage facilities were not initially designed to allow the removal of the waste, and in some cases they were seen as being the definitive waste disposal site. Examples include the Saint- Laurent-des-Eaux silos (BNI 74), the Orano plant silos in La Hague (silos 115 and 130 in BNI 38, the HAO silo in BNI 80), the pits and trenches of BNI 56 and the wells of BNI 72 and BNI 166. Retrieval of the waste from these facilities is complex and will span several decades. The waste must then be packaged and stored in safe conditions. New packaging and storage facilities are thus planned or under construction. With regard to the Effluent Treatment Stations (STE) which also packaged the concentrates, they were shut down owing to ASN Report on the state of nuclear safety and radiation protection in France in 2020 345 13 – DECOMMISSIONING OF BASIC NUCLEAR INSTALLATIONS 13